Fast scanning antenna with directivity corrective



Mmh24, 1964 TORU NOJI 3,126,546

FAST SCANNING ANTENNA WITH DIRECTIVITY CORRECTIVE GASEOUS CELL AT MOUTH OF HORN F iled Dec. 7, p55

2 Sheets-Sheet 1 FIG.3

TORU NOJI March 24, 1964 FAST SCANNING ANTENNA WITH DIRECTIVITY CORRECTIVE ,GASEOUS CELL AT MOUTH OF HORN 2 Sheets-Sheet 2 Filed Dec. 7, 1955 FIG.1a

3,125,545 Patented Mar. 24, 1964 3 125 546 rasr SCANNING AN'iiENNA wrrrr DIRECTIVITY CGRRECTIVE GASEOUS CELL AT MOUTH (IF HQRN Torn Noji, Huntington Station, N.Y., assignor to Hazeltine Research, Inc., Chicago, III., a corporation of iiiinois Filed Dec. 7, 1955, Ser- No. 551,708 4 Claims. (U. 3437tl1) This invention relates to high-frequency wave-signal antenna systems and, more particularly, to such antenna systems of the type useful in fast-scan radar equipment.

Heretofore, slow-scan radar equipments have, in general been designed with the scanning speed of the antenna system sufficiently low that the directivity characteristic of the antenna system during signal transmission and the directivity characteristic during signal reception inherently were substantially aligned. In fast-scan radar equipments, a scanning loss is introduced due to a displacement of the directivity characteristic during transmission with respect to the characteristic during reception. Such a scanning loss is particularly undesirable during reception of signals from the maximum range of the radar equipment because these are the weakest signals received.

It is an object of the present invention, therefore, to provide a new and improved high-frequency wave-signal antenna system which avoids the abovementioned disadvantage of prior such systems.

It is another object of the invention to provide a new and improved high-frequency waveignal antenna system useful in fast-scan radar equipment and capable of minimizing scanning loss.

In accordance with a particular form of the invention, a high-frequency wave-signal antenna system comprises a high-frequency wave-signal directive antenna including a horn having an opening for radiating high-frequency wave signals of high power and for intercepting high-frequency wave signals of low power. The antenna system also includes means disposed in the aforesaid horn opening and responsive to the aforesaid signals for altering the opening in accordance with variations of the power of the signals above and below a predetermined value for imparting to the antenna system different directivity characteristics with respect to a given antenna position for signals having power values above and below predetermined value, thereby to impart to the antenna system different directivity characteristics with respect to a given antenna position during translation of the radiated and intercepted signals.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

Referring to the drawings:

FIG. 1 is a diagrammatic representation of an antenna system, constructed in accordance with the invention, and its directivity characteristic during signal transmission;

FIG. 1a is a view of the antenna horn of the FIG. 1 system;

FIG. 1b is a diagrammatic representation of the antenna system of FIG. 1;

FIG. 2 is a diagrammatic representation of the antenna system to aid in explaining the operation, and

FIG. 3 is a diagrammatic representation of the antenna system and its directivity characteristics during reception.

Referring now more particularly to FIGS. la and 1b of the drawings, there is represented a high-frequency wave-signal antenna system comprising a high-frequency wave-signal directive antenna for radiating high-frequency wave signals of high power and for intercepting highfrequency wave signals of low power. The antenna preferably comprises a rotatable horn l0 and reflector 11, as represented in FIG. 1b. The horn 10 has an opening 12 for translating high-frequency wave signals of high and low power, as represented in FIG. 1a.

As also represented in FIG. la, there is provided impedance means disposed in the path of the signals and having different impedance values to signals having high and low power values for imparting to the antenna system different directivity characteristics with respect to a given antenna position during translation of signals having high and low power values, thereby to impart to the antenna system different directivity characteristics with respect to a given antenna position during translation of radiated and intercepted signals. As represented in FIG. 1a, this impedance means preferably comprises a gaseous medium 13 disposed in the opening of the horn 10 and appearing as a short-circuited element partially obstructing the opening to radiated signals having power values above a predetermined value and appearing as an open-circuited element to intercepted signals having power values below a predetermined value for altering the opening in accordance with the variations of the power of the signals above and below the predetermined value for imparting the above-mentioned directivity characteristics to the antenna system. This impedance means may comprise a gas similar to that used in TR tubes, such as hydrogen or argon enclosed in a suitable dielectric housing, for substantially aligning the directivity characteristic of the antenna system for intercepted signals returned from a predetermined range of the system with the directivity characteristic of the system for corresponding radiated signals.

As represented in FIGS. l3, inclusive, the antenna system preferably includes suitable means for rotating the antenna, such as a motor 14.

Considering now the operation of the antenna system with reference to FIGS. 1 and 1b, during transmission of the radiated signals of high power, the gaseous medium 13 becomes ionized and this effectively causes a short circuit to appear at the plane of the medium 13 at the mouth of the horn. This short circuit is reflected back into the horn and causes the effective center of the opening of the horn to move from point a to point b. The point of maximum intensity of the radiated signals as they strike the reflector 11 is, therefore, at point 0 which is displaced from the optical center d of the reflector. Accordingly, the signals are reflected from the reflector 11 with a directivity characteristic which is tilted with respect to the optical axis e following the path represented by the arrow 1.

Referring to FIG. 1, the directivity characteristic for high power signals is represented as displaced from the optical axis e of the antenna system.

In FIG. 2, the directivity characteristic for low power signals of the antenna system for the same antenna position as FIG. 1 is represented. This directivity characteristic is centered about the optical axis e because the gas medium 13 is deionized during reception of low power signals and the effective center of the horn Itl is at point a in FIG. 1b. Accordingly, the antenna system has different directivity characteristics for high and low power signals with respect to a given antenna position.

The motor M causes the antenna system to rotate at a high speed, for example 1200 revolutions per minute, and thus at the time that intercepted signals are returned from the maximum range of the system the antenna system has a directivity characteristic for received or low power signals which is substantially aligned with the directivity characteristic of FIG. 1 for radiated high power signals.

The dimensions and characteristics of the horn, reflector, and gaseous medium, and the speed of antenna rotation may be so chosen that the directivity characteristic for low power signals is substantially aligned with the directivity characteristic for high power signals at the time that intercepted signals are received from other than the maximum range of the system but, ordinarily, it will be desirable to align the directivity characteristics as previously explained because the power of signals returned from distances nearer the antenna system is greater than the power of signals returned from the maximum range of the system.

From the foregoing description, it will be apparent that an antenna system constructed in accordance with the invention has the advantage that the directivity characteristic of the antenna system for intercepted signals returned from a predetermined range of the system is substantially aligned with the directivity characteristic of the system for corresponding radiated signals, thereby reducing scanning loss.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A high-frequency wave-signal antenna system comprising: a high-frequency wave-signal directive antenna including a horn having an opening for radiating highfrequency wave signals of high power and for intercepting high-frequency wave signals of low power; and means disposed in said horn opening and responsive to said signals for alterin" said opening in accordance with variations of the power of said signals above and below a predetermined value for imparting to the antenna system diflerent directivity characteristics with respect to a given antenna position for signals having power values above and below said predetermined value, thereby to impart to the antenna system different directivity characteristics with respect to a given antenna position during translation of said radiated and intercepted signals.

2. A high-frequency wave-signal antenna system comprising: a high-frequency wave-signal directive antenna horn and reflector for radiating high-frequency wave signals of high power and for intercepting high-frequency Wave signals of low power; and impedance means disposed in said horn and having diflerent impedance values to signals having power values above and below a predetermined value for altering the opening of said horn in accordance with alterations of said impedance values to impart to the antenna system different directivity characteristics with respect to a given antenna position during translation of signals having power values above and below said predetermined value, thereby to impart to the antenna system different directivity characteristics with respect to a given antenna position during translation of said radiated and intercepted signals.

3. A high-frequency wave-signal antenna system comprising: a high-frequency wave-signal directive antenna including a horn having an opening for radiating highfrequency wave signals of high power and for intercepting high-frequency wave signals of low power; and impedance means comprising a gaseous medium disposed in said horn opening and appearing as a short-circuited element partially obstructing said opening to radiated signals having power values above a predetermined value and appearing as an open-circuited element to intercepted signals having power values below a predetermined value for alterning said opening in accordance with alterations of said impedance values to impart to the antenna system different directivity characteristics with respect to a given antenna position for signals having power values above and below said predetermined value, thereby to impart to the antenna system different directivity characteristics with respect to a given antenna position during translation of said radiated and intercepted signals.

4. A high-frequency wave-signal antenna system comprising: a rotatable high-frequency wave-signal directive antenna horn and reflector for radiating high-frequency wave signals of high power and for intercepting returned high-frequency wave signals of loW power; means for rotating said horn and reflector; and impedance means comprising a gaseous medium disposed in said horn and appearing as a short-circuited element partially obstructing said path to radiated signals having power values above a predetermined value and appearing as an opencircuited element to intercepted signals having power values below a predetermined value for altering the opening of said horn in accordance with alterations of said impedance values for shifting in the direction of rotation the directivity characteristic of the antenna system for signals of high power substantially to align the directivity characteristic of the antenna system for intercepted signals returned from the maximum range of the system with the directivity characteristic of the system for corresponding radiated signals thereby minimizing scanning loss.

Roberts July 14, 1953 Brown Feb. 14, 1956 

4. A HIGH-FREQUENCY WAVE-SIGNAL ANTENNA SYSTEM COMPRISING: A ROTATABLE HIGH-FREQUENCY WAVE-SIGNAL DIRECTIVE ANTENNA HORN AND REFLECTOR FOR RADIATING HIGH-FREQUENCY WAVE SIGNALS OF HIGH POWER AND FOR INTERCEPTING RETURNED HIGH-FREQUENCY WAVE SIGNALS OF LOW POWER; MEANS FOR ROTATING SAID HORN AND REFLECTOR; AND IMPEDANCE MEANS COMPRISING A GASEOUS MEDIUM DISPOSED IN SAID HORN AND APPEARING AS A SHORT-CIRCUITED ELEMENT PARTIALLY OBSTRUCTING SAID PATH TO RADIATED SIGNALS HAVING POWER VALUES ABOVE A PREDETERMINED VALUE AND APPEARING AS AN OPENCIRCUITED ELEMENT TO INTERCEPTED SIGNALS HAVING POWER VALUES BELOW A PREDETERMINED VALUE FOR ALTERING THE OPENING OF SAID HORN IN ACCORDANCE WITH ALTERATIONS OF SAID IMPEDANCE VALUES FOR SHIFTING IN THE DIRECTION OF ROTATION THE DIRECTIVITY CHARACTERISTIC OF THE ANTENNA SYSTEM FOR SIGNALS OF HIGH POWER SUBSTANTIALLY TO ALIGN THE DIRECTIVITY CHARACTERISTIC OF THE ANTENNA SYSTEM FOR INTERCEPTED SIGNALS RETURNED FROM THE MAXIMUM RANGE OF THE SYSTEM WITH THE DIRECTIVITY CHARACTERISTIC OF THE SYSTEM FOR CORRESPONDING RADIATED SIGNALS THEREBY MINIMIZING SCANNING LOSS. 